Cooperative vehicular safety technology provides full vehicle driving safety service by using short-range wireless communication. Regarding to the cooperative vehicular safety technology, it requires every vehicle periodically broadcasts current state information itself, which includes vehicles location itself, driving direction, speed, driveway, model, signature, etc, for reminding drivers to avoid the view mismatch and dead space. Additionally, the cooperative vehicular safety technology also requires every vehicle immediately broadcast emergency events (for example, emergency brake, driveway change, turn, overtaking, etc.), for informing the affected neighboring vehicles to avoid the car crash and traffic accident.
General speaking, wireless transmitting power control is only used to operate transactions between the base station and the mobile devices or among the mobile devices. Firstly, the transmitting power may be enclosed in a packet, and then the base station sends a packet to the mobile device. Subsequently, the mobile device measures the received signal strength and calculates the signal strength path loss model at the mobile device according to the transmitting power and the received signal strength. Afterward, the mobile device returns the results about the signal strength path loss model to the base station. Similarly, the base station also performs the process as similar as the mobile device and calculates the signal strength path loss model at the base station and returns the results about the signal strength path loss model to the mobile device. Thereby, this interchange process is alternately performed for obtaining optimal transmitting power. With regard to the transmission of transaction among the mobile devices, the interchanged processes are similar as transmission of transaction between the base station and the mobile.
However, the cooperative vehicular safety technology requires each vehicle regularly broadcasts current state information itself to its neighboring vehicles. Thereby, the conventional transmitting power control can not apply in the cooperative vehicular safety technology. In addition, it must consider problems, such as the vehicle speeding, the network topology changing, and difficult traffic density (the number of flowing vehicles/lane) calculating. Moreover, the cooperative vehicular safety technology does not have the transaction concepts, and therefore it can not teach or warn devices how to properly use the transmitting power, and when a driver use the cooperative vehicular safety technology to inform other drivers, and the other drivers can not answer the driver by using the proper transmitting power. As a result, the cooperative vehicular safety technology only uses the largest transmitting power to send information, and the efficiency of wireless frequency usage in the space will be poor and the chance of the signal interferences and the packet collisions will be increased if the vehicle drives in the heavy traffic or crowded area including vehicles sending the information by using the largest transmitting power. Taking IEEE 802.11p/IEEE 1609 for an example, the largest effective range is approximately 500 meter. Therefore, in the metro area with four-lanes highway and the largest effective transmission radius is 500 meter, it almost approximately has two hundreds cars to rival the wireless channel when the heavy traffic or high-density vehicle flow, resulting in serious packet interferences and collisions are occurred.